Fine Assessment of Water Abundance and Water Inflow Potential in Coal-Bearing Strata Based on Water Storage Space Microelements

Mine water inflow is one of the primary hazards threatening the safety of coal-mining production. Groundwater in coal-bearing strata serves as the direct water-filling source for coal mining, and its water abundance significantly impacts the intensity of the mine water inflow. The coal-bearing strata in the Ordos Basin, China, were formed during the Jurassic period, and the coal measure sandstones are characterized by short diagenetic times, weak cementation, and significant variations in the water abundance. This paper analyzes the paleosedimentary environmental characteristics of the coal-bearing strata in the study area, revealing the distribution of sedimentary facies and their water-controlling rules. Combining cast thin section (CTS) and nuclear magnetic resonance (NMR) analyses, the porosity, pore structure, and connectivity characteristics of sandstones with different grain sizes were investigated. Utilizing fractal theory, the coal-bearing strata were three-dimensionally discretized to obtain water storage space microelements. By statistically analyzing the proportions of sandstones with varying grain sizes within the microelements and integrating porosity characteristics, the comprehensive water storage space of the microelements was derived. Finally, based on the sandstone water storage microelements, a three-dimensional evaluation of water abundance and an assessment of water inflow potential in the coal-bearing strata were conducted. The results indicate that sandstone aquifers are widely developed within the sedimentary paleochannels in the study area, exhibiting strong water abundance and excellent connectivity, thus serving as dominant runoff channels for groundwater. The porosities of coarse, medium, and fine sandstones were 21.07%, 17.31%, and 10.2%, respectively. The water storage space of the microelements within the coal-bearing strata ranges from 600 to 1700 m³, peaking at 1400-1700 m³ within the 20-40 m and 80-100 m horizons above the coal seam roof, which are classified as strong water-rich zones. The water abundance evaluation based on water storage microelements demonstrates high consistency with the exploration results derived from 3D seismic multiattribute fusion; based on this, a fine assessment model for water inflow potential was established. The research findings provide a novel methodology for predicting water abundance and evaluating the water inflow potential in weakly cemented coal-bearing strata.